Equilibrium and Kinetic Studies of Adsorptionof Cd21 and Pb21 Ions from Aqueous Solutionby Citric Acid Modified Maize Fibres

Abstract

Maize fibres were pre-treated and chemically modified with 0.05 M citric acid. The adsorption of Cd21 and Pb21 ions onto the citric acid modified maize fibres was studied in batch experiment at ambient conditions. The study showed that the adsorption of Cd21 and Pb21 ions depends on metal ion concentration, adsorbent dosage and contact time. Langmuir and Freundlich adsorption models were used to model the equilibrium data. Based on linear regression value r2, the adsorption fits Langmuir adsorption model well compared that of Freundlich. The maximum binding capacity of the metal ions as obtained from the Langmuir fit were 4.93 and 4.88 mg g21 for Cd21 and Pb21 ions, respectively. The value of Freundlich constants, n and kF, obtained from Freundlich fit were 2.63 mg g21 and 0.60 for Cd21 and 2.79 mg g21 and 0.68 for Pb21. The rate constant and r2 values as obtained from pseudo first-order, pseudo second-order and intra-particle diffusion plots were 2.6 3 1022 min21, 0.997; 9.7 3 1022 g mg21 min21, 0.985 and 2.6 3 1022 min21, 0.997, respectively, for Cd21, while those for Pb21 were 2.6 3 1022 min21, 0.993; 7.1 3 1022 g mg21 min21, 0.990 and 2.6 3 1022 min21, 0.993, respectively. The r2 values showed that the metal ion adsorption onto citric acid modified maize fibres follows pseudo first-order kinetics and is controlled by intra-particle diffusion. This study suggests that citric acid modified maize fibres can be used in simple water treatment units to remove Cd21 and Pb21 ions.